Polymeric prosthetic liners (or “liners”) have become the interface of choice among amputees due to various beneficial characteristics thereof. These characteristics include, for example, comfort, security of suspension, protection of the residual limb, and ease of use. Modern liner technology allows amputees to employ a liner as the sole (stand-alone) interface between their residual limb (which is also commonly referred to as a residuum or amputation stump) and the interior of a prosthetic socket—in contrast to known wool or knit socks and cushioned socks or sheaths that must be worn in multiple layers and/or various combinations to provide sufficient cushioning and protection to a residual limb.
Prosthetic liners may be non-suspensory in nature. Non-suspensory liners are commonly referred to as “cushion liners.” Prosthetic liners may optionally be suspensory in nature and may, therefore, include a docking element that facilitates suspension by mechanical attachment of the liner to a prosthesis. Suspensory liners are commonly referred to as “locking liners.” Liners can be of standard “off-the-shelf” design, meaning the liner is of generic shape and will fit a range of residual limb shapes and sizes. Alternatively, liners may be custom designed for a particular amputee.
Liners may be comprised of various polymeric materials, including silicone, urethane, and thermoplastic elastomers (TPE) gels. Liners are now commonly made using various block copolymer and mineral oil gel compositions. Such polymeric materials, particularly block copolymer and mineral oil gel compositions, have proven themselves to provide an optimal level of comfort for most users.
It is also known to construct such liners with an outer layer of fabric. That is, there exist patented fabric-covered liners having an interior of exposed polymeric gel for contacting and cushioning an amputee's residual limb, and an outer layer of fabric for, among other things, increasing the wear resistance of the liner, and facilitating donning/doffing and insertion of the liner-covered residual limb into a prosthetic socket. Such patented fabric-covered liner products are available from The Ohio Willow Wood Company in Mt. Sterling, Ohio.
While polymeric gel materials provide amputees with a great deal of cushioning and comfort, it is well known that such gels are also highly stretchable. The stretchable nature of such gels allows a liner constructed therewith to conform well to residual limbs of different shape. However, and particularly with respect to locking liners or cushion liners used with vacuum suspension systems, the stretchable nature of these gel materials may allow for the associated liner to stretch to an undesirable degree along the length of the residual limb (i.e., in a longitudinal direction).
To this end, it is desirable to limit the longitudinal stretch of a prosthetic liner. One complicating factor in this regard is that any longitudinal stretch limiting technique employed must not significantly limit the ability of the liner to stretch radially (i.e., circumferentially). Some degree of circumferential stretch is required in order for a liner to accommodate residual limbs of different diameter while still maintaining an intimate fit therewith. Some amount of longitudinal stretch is also required for limb accommodation purposes. Consequently, employing a technique that overly inhibits stretching of a liner in a circumferential direction or that completely prevents stretching of a liner in a longitudinal direction is generally unacceptable.
As would be understood by one of skill in the art, liners as described above are frequently used by lower limb amputees. Lower limb amputees generally fall into one of two categories: above knee (AK) amputees and below knee (BK) amputees. In the case of a BK amputee, the knee joint is still present and, thus, a bending of the residual limb at the knee joint will still occur during ambulation. While the prosthetic hard socket of a BK prosthesis is generally recessed to accommodate the knee joint, BK amputees typically wear a liner that extends over the knee joint to some point along the thigh of the residual limb. Consequently, bending of the knee joint occurs under cover of the liner.
As should be apparent, the use of liners by BK amputees presents yet another problem when attempting to limit the longitudinal stretch of a liner. Particularly, because the knee joint bends while covered by the liner, and because the polymeric gel of the liner clings to the skin of the residual limb, providing a BK amputee with a liner that exhibits no longitudinal elasticity or that has overly limited longitudinal stretch characteristics, can hinder or render uncomfortable bending of the knee joint. This may result from the knee joint struggling to stretch the liner and/or from the polymeric gel material pulling against the skin of the anterior portion of the knee joint. In any event, considerable pressure can be applied to the patellar area of the knee joint if a liner inhibits knee flexion. As would be apparent, a similar problem would exist in the case of a liner that covers the elbow joint of an upper extremity amputee.
Various techniques have been proposed and employed in an attempt to restrict longitudinal liner stretch to an acceptable degree. These techniques have included, without limitation, embedding a reinforcing mesh or wires in the polymeric material at the distal end of the liner, attaching strips of material of limited longitudinal stretch to the exterior of the liner, and covering the entire liner with a material (e.g., fabric) that exhibits no stretch or much less stretch than the polymeric gel portion of the liner. None of these techniques have provided acceptable results. The embedment or attachment of reduced stretch materials to a liner has proven ineffective at controlling the overall longitudinal stretch thereof. Further, known liners having an embedded mesh at the closed end have also exhibited greatly reduced stretch in the radial or circumferential direction. Covering an entire liner with a non-stretch material or a material of greatly reduced stretch is undesirable for the reasons articulated above.
It can be understood from the foregoing discussion that there is a need for a polymeric gel liner that exhibits limited and controlled longitudinal stretch characteristics without adversely affecting other liner characteristics or user comfort. Liners of the present invention satisfy this need.